1. Field of the Invention
The present invention relates to treating exhaust gases of an internal combustion engine to reduce pollutants therein and, more particularly, to a system and method using water vapor condensed from the exhaust gases to producing a reducing agent introduced into the exhaust flow.
2. Description of Related Art
Devices for removing nitrogen oxides (xe2x80x9cNOxxe2x80x9d) from the exhaust gas of an internal combustion engine, particularly a diesel engine, are known. This is referred to as denitrizing or xe2x80x9cdeNOxingxe2x80x9d the exhaust gas.
A system disclosed in EP 0 577 853 B1 has an engine that includes an exhaust pipe, a deNOx catalytic converter connected to the exhaust pipe, a tank for a reducing agent which can be at least partially converted into ammonia, an ammonia generator connected upstream of the deNOx catalytic converter, and a device for introducing the reducing agent into the exhaust gas flowing to the deNOx catalytic converter. In the deNOx catalytic converter, selective catalytic reduction (SCR) takes place, with ammonia as an agent for reducing to nitrogen the nitrogen oxides in the exhaust gas.
In this device the ammonia may be generated from a nontoxic precursor substance, such as urea. In such a case, the ammonia used for the SCR reaction is formed by hydrolysis from an aqueous urea solution. The hydrolysis may take place by direct injection of an aqueous urea solution into the hot exhaust gas or by bringing the aqueous urea solution into contact with a hydrolysis catalyst. It is possible to use an aqueous urea solution of from 20 to 60% strength.
In another system, disclosed in DE 30 02 871 A1 (GB 2,068,259 A), a diesel engine exhaust pipe is connected to a device for cleaning the engine exhaust gas. A condensation water collector connected upstream of the device is in fluid communication with the exhaust pipe. However, the cleaning device in this system is a sorption filter.
An object of the invention is to provide an exhaust system of an internal combustion engine having a particularly compact device for cleaning the exhaust gas from the internal combustion engine.
A further object of the invention is to provide an effective, inexpensive method for reducing pollutants in the exhaust gas from the internal combustion engine, in which method the exhaust gas is fed via an exhaust pipe to a device for cleaning the exhaust gas.
In accordance with one aspect of the invention, an exhaust system for an internal combustion engine having an exhaust pipe for moisture-containing engine exhaust gas and a catalytic converter connected to the exhaust pipe for cleaning the exhaust gas in the presence of a reducing agent comprises a condensation water collector for accepting the exhaust gases and condensing moisture therein as liquid water condensate, a reservoir for holding the water condensate, and a storage chamber for incorporating the water condensate into an aqueous solution of a reactant for introduction into the exhaust pipe to provide the reducing agent.
In accordance with another aspect of the invention, a method for reducing pollutants in internal combustion engine exhaust gas containing moisture comprises the steps of directing at least a portion of the exhaust gas to a condensation water collector for condensing moisture in the exhaust gas as liquid water condensate, combining the water condensate with an aqueous solution of a reactant capable of forming a reducing agent, and introducing the aqueous solution into the exhaust gas prior to the entry of the exhaust gas into a catalytic converter for cleaning the exhaust gases in the presence of a reducing agent.